On Friday, the U.S. Treasury Department released guidance on President Trump’s Executive Order on payroll tax deferral, just days before the Tuesday start date for the deferral period. You can also view additional information on the guidance from Littler here.

Under the guidance, employers can opt to not withhold Social Security payroll taxes from their employees’ paychecks from September through December. To pay the amounts that were deferred, the amount of Social Security payroll taxes withheld from employees’ paychecks would increase from Jan. 1 through April 30. Employers can only defer payroll taxes for employees who make less than $4,000 on a biweekly basis.

At this time, a number of business groups have raised concerns about the order, arguing that there are some uncertainties about how it would apply and that a deferral could be challenging for employees who could face more taxes next year. Many businesses are not expected to implement a deferral, and are expected to continue to withhold payroll taxes from their employees’ paychecks. Tax experts have also said the guidance leaves a number of key questions unanswered, such as what happens if an employee leaves a company before April 30, and how the guidance applies to seasonal workers and employees with irregular hours.